Transcript Species and Evolution

A Brief History of Biology
Black Boxes Within Black Boxes
or
Wheels within Wheels
The Age of Naked Eye Investigation
• Around 400 BC certain texts attributed to Hippocrates described
certain ailments and attributed them to diet and other physiological
causes
• Living matter believed to be made of four humors: blood, yellow bile,
black bile, and phlegm
• Aristotle investigated nature in a systemized manner, developing
categories for life (many of which are still used)
• Galen, a Roman physician (200 AD), attempts to understand life
through dissection. He determined that the heart pumped blood, but
not that it circulated (this was only discovered in the 17th century by
an Englishman, William Harvey.
• Biology, essentially didn’t advance until the 17th and 18th centuries
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The Age of the Microscope
Galileo uses a microscope to observe the compound eye
of insects
Several others followed observing capillary blood flow,
micro organisms, cells in cork and leaves, etc.
Early 19th century: The Cellular Theory of Life was
proposed by Schleiden and Schwann: that all life was
based on cells and cellular secretions, also that cells
have a life of their own despite their part in larger
organisms
Cells looked very simple at this time and its function
was assumed to be simple
It was discovered, by Wohler in 1828, that living matter
is made of the same fundamental stuff as non living
matter
Limits to the Microscope
• For physical reasons a microscope cannot resolve two points closer
together than ½ the wavelength of light
• Most structures in cells are too small to be seen with these
microscopes and eluded discovery
• After WWII the electron microscope was developed and the cellular
world was found to be more complex than ever imagined
• The ultimate function lay beyond even what could be seen with the
electron. Life is based on Molecular Machines
• Proteins, the building blocks and building machines, of life were
modeled… and found to be incredibly complex
– “Could the search for ultimate truth really have revealed so hideous and
visceral-looking an object?” – Max Perutz 1958
• DNA, not protein, is discovered to be the blue print for life
The Inner Life of A Cell
http://multimedia.mcb.harvard.edu/ (narrated)
http://aimediaserver.com/studiodaily/videoplayer
/?src=harvard/harvard.swf&width=640&height
=520 (unnarrated)
Classification
Taxonomy and Phylogeny – lending
order to investigation
• Species (from the Latin: kind): A group whose
members posses similar anatomical characteristics
and have the ability to interbreed.
• Speciation: The evolution of a new species
• Taxonomy: The branch of science concerned with
naming and classifying the diverse forms of life.
• Phylogeny: the sequence of events involved in
the evolutionary development of a species or
taxonomic group of organisms
• Linnean System – Binomial Nomenclature
How many species are there?
- about 1.8 million species
have been given scientific
names
- nearly 2/3 are insects
- estimates of the total number of living species generally
range from 10 to 100 million (most are insects and
microbes)
Linnaean system of classification
-used in the biological sciences to describe and categorize
all living things
- Taxonomy - classification of organisms into different
categories based on their physical characteristics; used
before genetic testing
The Linnaean system uses two Latin name categories
(genus and species) to designate each type of organism
- genus: higher level category that includes one or more
species under it
Referred to as binomial nomenclature
Ex: Humans are (genus) Homo (species) sapiens (“man
who is wise”)
Biologists classify organisms into different categories by
judging degrees of similarity and difference that they can
see
- the assumption is that the greater the degree of physical
similarity, the closer the biological relationship
Homologies
A homology is a character shared between species that was also
present in their common ancestor; the more homologies, the
more closely related
Problems with homologies
Convergence: species from different evolutionary
branches may come to resemble each other if they live in
similar environments
Analogies: anatomical features that have the same form or
function in different species that have no known common
ancestor
Classification
• The Pneumonic
– King Philip Came
Over For Good Sex
Shark
Dolphin
Kingdom:
Animalia
Kingdom:
Animalia
Phylum:
Chordata
Phylum:
Chordata
Subphylum:
Vertebrata
Subphylum: Vertebrata
Class:
Chondrichthyes
Class:
Mammalia
Evolution
Introduction: Charles Darwin 1809 1882
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He studied medicine at Edinburgh University
Then theology at Cambridge
During his five-year voyage on the Beagle he
established himself as a geologist
He published journals of the voyage, making
him a popular author
He was intrigues with species diversity and
conceived his theory of natural selection in
1838
In 1858 Alfred Wallace sent him an essay
describing his idea, which prompted a joint
publication
In 1859 he published: On the Origin of
Species
Since that time evolution from common
descent has been accepted as the dominant
explanation of diversity in nature.
Though reticent about his religious views, in
1879 he responded that he had never been an
atheist in the sense of denying the existence
of a God, and that generally “an Agnostic
would be the more correct description of my
state of mind.”
Darwin’s Ideas
• The Observation
– That species change over time
• The Implication
– Perhaps all living species arose from earlier forms
• What he knew nothing about
– Genetics
– Mechanisms of Inheritance
• What he never saw in his life
– Irrefutable proof
Darwin’s Evidences
• He noted that South American fossils were
more similar to present day South American
species than to the species of other continents.
• He read Charles Lyell’s work, Principles of
Geology, and was introduced to Gradualism.
• Noted how species on the Galapagos Islands
are unlike those anywhere else.
• He hoped to find extensive evidence of this in
the fossil record.
Is this a New Idea?
• Anaxiamander (500 BC) believed life arose from water and that simpler
forms of life preceded more complex ones
• However, Aristotle taught that species were unchanging. His logical
conclusions dominated the theological thinking of the three great Western
Patriarchal religions: Judaism, Islam, and Christianity.
– An aside: The Holy Scriptures of these religions don’t say species can’t change,
rather the men interpreting those scriptures said it.
• In the 1700s fossil studies began to suggest that the earth was older than
6000 years
– An aside: The Holy Books describe creation occurring in segments described
as days, which could be of any length of time since the sun was not made until
the 3rd.
• French naturalist, Georges Buffon, suggested that these fossils may be
earlier forms of current species.
• Lamarck’s theory of Evolution (1802): Using or not using body parts leads
to inheritance of those parts
Two Theories of Note
CATASTROPHISM
• The idea that Earth has been
affected in the distant past
by sudden, short-lived,
violent events that were
sometimes worldwide in
scope
GRADUALISM
• From 1850 to 1980 scientists
rejected catastrophism
• Instead they believed that the
earth had been shaped by the
long term action of forces such
as volcanism, earthquakes,
erosion, and sedimentation,
that could still be observed in
action today.
• Darwin’s thinking about
species formation was
essentially gradualism in
biology.
Changes in Thinking
• Catastrophism reevaluated in the 1980s due to
new discoveries and the implications of
modeling systems.
Luis Alvarez Impact Event Hypothesis
It is believed that a 10km asteroid struck the earth 65 million years ago
and ended 70% of all species of the Cretaceous period, including
dinosaurs.
The Current Theory of Lunar Formation
Currently, the only viable explanation of the presence of earth’s massive moon
is the near miss of a Mars sized planetesimal 4.5 billion years ago. The resulting
debris formed an accretion disk which the moon formed from.
Evidences of Evolution
The Fossil Record
• Currently considered the best evidence of species
evolution
• It demonstrates a historic sequence in the appearance of
species
– Less complicated life forms predate more complicated ones
– The oldest fossils are prokaryotes (bacteria), dated 3.5
billion years
– Fish are the oldest vertebrates
• Despite this order, transitional species are almost
completely absent in the fossil record
Other Evidences
• Biogeology – The similarity and specificity of organisms in isolated
regions
• Comparative Anatomy – Body structures in different species.
Anatomical similarities among many species indicate common
descent.
– Homologous Structures: Features with different functions but structural
similarity due to common ancestry
– Analogous Structures: Features with structural similarity due to similar
environmental pressures yet the species in question have no ancestral
relation
• Comparative Embryology – Closely related organisms often have
similar stages in embryonic development
• Molecular Biology – The universality of genetic code allows
species to be compared on a molecular basis.
– Hemoglobin Comparisons
Homologous Structures
Features with different functions but structural similarity due to common
ancestry
Analogous Features
Features with structural similarity due to similar environmental pressures
yet the species in question have no ancestral relation
Comparative Embryology
Closely related organisms often have similar stages in embryonic
development
Molecular Biology
The universality of genetic code allows species to be compared on a
molecular basis
Hemoglobin Comparisons
This complicated protein is used in many species to carry oxygen
molecules. The sequence of amino acids (the building blocks of proteins)
varies more the father separated species are.
The Darwinian Mechanism:
Natural Selection
Natural Selection
Organisms are in competition due to
environmental pressures and limited resources
• Natural Selection – The fittest will breed most
• Artificial Selection – Human manipulated
selective breeding
– Domesticated animals
– Domesticated plants
• Example: Insect resistance to pesticides
• Example: Bacterial resistance to antibiotics
Definitions
• Population: A group of individuals from the same
species, living in the same space, at the same
time.
• Species: A population of individuals with the
ability to interbreed and produce fertile offspring.
• Gene Pool: The sum total of a population’s DNA.
• Microevolution: The change in the frequency of
alleles in a population’s gene pool.
• Macroevolution: That change of one species into
another.
Evolutionary
Trees
Using either physical
features or molecular
analysis species can
be classified into
branching family
relations. In essence,
this is a hierarchy of
complexity.
Micro Evolution
Species Change over Time
Microevolution
•Species change
over time
•These changes
may occur
naturally or they
may be induced
by human
interaction
Non Evolving Populations
The Gene Pool of non Evolving populations
remains constant
• Sexual reproduction alone does not lead to
microevolution; it merely shuffles the genes
• Gene Pool: all of the various genes in any
member of a species anywhere
An Example
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Humans have two copies of almost
every gene (23 chromosomes from
each parent)
Let us imagine genes to be cards,
each card representing a certain trait
The cards come from the card pool
As long as the cards say the same
thing I am not evolving
For example, you get two cards for
eye color, but there are more than two
eye colours out there
A human genome contains only about
30,000 genes; though that number is
being debated
We get a huge variety of hands, but
that’s just the luck of the draw
For microevolution to occur
something must change a card itself
or cause a certain card to appear more
or less frequently
Hardy Weinberg Equilibrium
5 conditions must be met to keep a gene pool
constant
1. A Large Population
2. The Population is Isolated
3. Mutations do not alter the Gene Pool
4. Mating is Random
5. All individuals are Equal in Reproductive
Success
Causes of Microevolution
• Genetic Drift: A completely random process. Any
small portion of a population may not represent allele
frequencies well
– Example: Coin Tosses
– Bottleneck Effect: Drift caused by an event, which
drastically reduces population size. Catastrophe or
colonization can cause this.
– Founder Effect: A small group of colonizers which breed
largely with themselves (Amish, European Nobles)
– Gene Flow: Fertile individuals moving in and out of
populations. It reduces genetic differences. (Spain and
Southern Italy)
Causes of Microevolution
• Natural Selection: The only process which
allows adaptive change in a species.
– Question: Do beneficial genetic advantages always
lead to improved breeding?
• Mutation: The ultimate source of new genetic
information.
– With the previous two we have only changed the
frequencies of the “cards.”
– This mutation must produce a new allele.
– Natural mutations occur in DNA sequences once in
100,000 to 1,000,000.
Variation and Natural Selection
• Not all variation in populations is inheritable
• Polygenetic Inheritance: When multiple genes affect one trait
– Hair color
• The offspring of species vary due to two processes: Gene shuffling
and mutation
– Both processes are completely random
– Selection only affects a gene if it’s manifested, ergo recessive traits
cannot be influenced by natural selection
– Mutation is almost always harmful
• When a mutation leads to improved breeding this gene will become
more common in the species.
– Bacterial resistance
• Endangered species suffer from a lack of genetic diversity
– Cheetahs and Bananas
Survival of the Fittest?
• Direct competition between members of a species
for reproductive privileges is relatively rare
• Survival alone does not guarantee reproductive
success
– The biggest, toughest, fastest frog in the pond has a
fitness of zero if he’s sterile
• Darwinian Fitness: The contribution an individual
makes to the gene pool of the next generation
relative to the contribution of other individuals
– Implication: The fittest individuals are those who pass
on the greatest number of genes to the next generation
The Observable Outcomes of
Natural Selection
Stabilizing Selection
What usually occurs in stable populations. The extremes are culled.
Example: Brown Trees and Brown moths.
Directional Selection
Eliminates individuals at one of the extremes. Occurs during periods of
environmental change.
Example: Taller trees and giraffe necks.
Divergent Selection
Extreme individuals are favored.
Example: Short billed ducks and long billed ducks.
Sexual Dimorphism
• The secondary sexual
characteristics between
males and females
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Size
Color
Behavior
Adornment
• Generally, males are the
showier sex in nature and
use appearance or
behavior to attract females
Darwin’s Concern
• Fascinatingly, showy plumage and adornment
offers no survival advantage and would be
reinforced only by choice.
• In these instances successful breeders are less
fit for their environments
• Since we preserve the weakest of our species,
Darwin was concerned that we have
effectively halted beneficial evolution.
Selection Cannot Fashion Perfect
Organisms
1. Historical Constraints
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Evolution cannot scrap ancestral forms
Features can be modified only slowly
2. Adaptations are Compromises
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Features usually have several functions as an organism must do
several different things to survive
3. Not all Evolution is Adaptive
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Chance is the governing role in mutation and species adapted
to a particular region are often relocated to random ones
4. Selection only Edits
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Only the fittest phenotypes are selected, which may not be
ideal ones.
Macro Evolution
Particles to People
Macro Evolution
• It is proposed that microevolutionary changes
will induce speciation events given sufficient
time
• It is assumed that all organic life is descended
from one simple life form
• Speciation events are not generally observable
– The London Mosquitoes
Darwinian Evolution Modified
• Darwin believed that species evolve steadily,
slowly, and predictably
• Due to that he predicted seeing a steadily
changing fossil record
• This was not found, rather we see distinct species
• Occasionally we see massive destructive periods
where large numbers of species are wiped out, in
the aftermath we see many new species arriving
Revising Things
Punctuated Equilibrium
• In the past 50 years, some evolutionary biologists,
frustrated by the lack of transitional forms,
developed a new hypothesis
• The hypothesis is known as punctuated
equilibrium and describes evolution moving in
spurts, with new species diverging abruptly
• The other theory about the gaps in fossil records
is that the intermediate species in question
migrated, thus eluding fossil detection in that
region
Punctuated Equilibrium
The idea was put forth in 1972 to describe gaps in the fossil record
The Molecular Question
• In the past 20 years we have gained considerable
understanding about several cellular processes and
machines on a molecular level
• Cells are profoundly complex and mechanistic
• Models for the generation of simple cellular machinery
from preexisting material are under debate
• Pathways are suggested, but none have been accepted
• This is a region of current research
• Previously, arguments focused on anatomical
similarities
Simple to Complex Eyes
• It has been argued that
human eyes are
irreducibly complex
• It is clear from anatomical
investigations that there
are many simpler eyes
than human eyes
• Human eyes, then, may be
the most current in a
series of anatomical
jumps
The Molecular Question
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Even the simplest eyes rely on the same complicated molecular process
Where did this process come from?
There are no simpler forms of light detection
Currently there are no models of step wise evolution to a photo receptor
The Miller Experiment
• Conducted in 1952 by Stanley
Miller
• An investigation of the ability
of simple molecules to
organize into amino acids, the
building blocks of protein
• Early earth gasses were placed
in a flask and subjected to
electric shock resulting in the
amino acids
• The early atmosphere is
presently debated, nitrates will
destroy amino acids as will O2
• Even with amino acids, they
must be in correct sequences to
do anything, and in a
membrane
Suggestions on the Origin of
Simple Cells
• We need data storage and replication
for life
• That means RNA or DNA
• Present cells process information:
– DNA to RNA to Protein
• Certain RNA sequences can self
replicate without proteins
• Some lipids spontaneously form
spheres
• Perhaps RNA entered on of these
spheres in the right configuration to
induce replication
• These amalgamations of cooperating
molecular materials are called Coops
The Geological Timeline
• In Geology it is assumed that appearance in time is related
to position in rock strata
• There is a sequence to the appearance of life forms
• Generally, simple organisms predate more complex ones
• It is proposed that all forms of life now existent come from
a single precursor
• Geologists have assembled time table describing these
trends
• Radiometric Dating is used to estimate the ages of fossils
• The half life of 14C is about 5,730 years, therefore that is
the limit of our resolution
Continental Drift
• Anciently the continents
were together
• This was called, Pangea
• Slowly, they are drifting
apart; about 2cm per
year
• Species trapped on these
continents have been
evolving separately